This application claims the priority of German Patent Application Serial No. 100 06 253.9, filed Feb. 11, 2000 the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to agitator assemblies, and more particularly to an agitator assembly of a type having one or more sweep blades mounted at a motor driven shaft and operating in an agitation vessel.
Agitator assemblies of this type are typically used for mixing, granulating and drying solid matter. In this case, it is desirable to avoid inadequate or insufficient mixing during agitation. Furthermore, if agitation is carried out for drying solid matter, agitation should not only provide proper mixing of the solid matter but, in addition, should also provide a high degree of heat transfer during the process of agitation. Thus, it is desirable that agitation performing a high degree of mixing the solid matter is provided and that also a high degree of heat transfer within the agitated material is realized.
Apart from heating or cooling solid matter, such an agitator assembly may also be useful for carrying out chemical reactions, for volatilizing solvents, and for crystallization through evaporation or cooling.
It would be desirable and advantageous to provide an improved agitator assembly for agitation of solid matter in an agitation vessel such as to provide a high degree of mixing and a high degree of internal heat transfer.
According to one aspect of the present invention, an agitator assembly is provided which includes a vessel; and an agitator received in the vessel and having at least one sweep blade, with the sweep blade ascending from an inner zone of the vessel to an outer zone thereof at an angle of inclination ranging from about 15xc2x0 to 60xc2x0 with respect to a horizontal.
Suitably, the inner and outer peripheral edges of the sweep blade is configured in an elliptical shape. The sweep blade may have a minimum width at its lower end and a maximum width at the upper end.
In a configuration of the agitator assembly with more than one sweep blades, at least one of the sweep blades may be provided with a bottom blade mounted at the lower end of the sweep blade and serving as a bottom clearer of the agitation vessel. The bottom blade may be attached with its upper end to the lower end of the sweep blade and is suitably so configured that its maximum width is at the upper end and its minimum width is at its lower end. Advantageously, the bottom blade may be formed in a helical shape and mounted relative to the horizontal at an angle in a range from 5xc2x0 to about 55xc2x0 and increasing from the lower end to the upper end.
According to another feature of the present invention, the sweep blade is provided at its upper end with a side blade, which is suitably of flat configuration and attached to the sweep blade at an angle of inclination from about 1xc2x0 to about 30xc2x0 relative to the vertical. The side blade may also be attached to the sweep blade at a clearance angle of about 1xc2x0 to about 30xc2x0 with respect to the inner wall of the agitation vessel.
The side blade may have a leading edge which is positioned at a substantially constant distance from the cylindrical inner wall of the agitation vessel, with the distance ranging approximately from 5 mm to 10 mm. Suitably, the leading edge of the side blade has an elliptical shape.
According to a further feature of the present invention, a baffle may be arranged above the sweep blade, with the baffle having a lower edge extending relative to the horizontal at an angle from about 15xc2x0 to 60xc2x0. The baffle is suitably oriented relative at an angle from about 0xc2x0 to about 75xc2x0 to a radial line which extends through a center axis of the baffle and through a center axis of a driveshaft by which the agitator is driven. Suitably, the driveshaft is installed in overhead configuration so that no bearings or seals are required in the product zone.
According to a further feature of the present invention, at least one motor-driven crusher may be mounted above the sweep blade, with the crusher having one end carrying a plurality of knives. The circumferential speed of the crusher is suitably in the range of about 15 m/sec.
According to a further feature of the present invention, the agitation vessel is configured with an upper cylindrical portion and a lower conical bottom portion connected to the upper portion and having a cone angle in the range of about 60xc2x0 to about 120xc2x0, preferably a cone angle of 90xc2x0. Suitably, the sweep blades are disposed in the conical bottom portion of the agitation vessel. The upper cylindrical portion and the lower bottom portion have heights at a ratio of about 1:1 to about 2:1.
With the agitator assembly according to the invention, a complete circulation of product material is realized, resulting in a high degree of product mixing. A high degree of product mixing provides a high rate of heat transfer and an even temperature level among the product, thus leading to an extensive product surface regeneration and accomplishing good discharge of the product without leaving recondensation on the cooler product. In turn, the high heat transfer surface leads to shorter drying and cooling sessions. In conjunction with the baffles and the crushers, the sweep blades of the agitator assembly according to the present invention, bring about a good coarse comminution and a rapid and easier break up of clumps and lumps.
An agitator assembly according to the present invention is thus capable to also disperse agglomerates or to produce granulates, and to agitate doughy or waxy masses. It is therefore not only suitable for flowable products but also for use with those materials that have a doughy consistency and with those that form clumps at drying, as oftentimes encountered in the pharmaceutical industry.